docs: def upsert_event(self, calendar_id, event):
          """Inserts or updates an event for the specified calendar.
  
          :param string calendar_id: ID of calendar to insert/update event into.
          :param dict event: Dictionary of event data to send to cronofy.
          """
          event['start'] = format_event_time(event['start'])
          event['end'] = format_event_time(event['end'])
          self.request_handler.post(
              endpoint='calendars/%s/events' % calendar_id, data=event)